The present invention relates to the estimation of extant battery life for battery powered apparatus.
Mobile telephones are an example of a battery-powered device familiar to most people. The extant battery life of battery-power devices, including mobile telephones, is of considerable importance to their users. Consequently, the provision of extant battery life indicators on mobile telephones is universal.
One method of determining the extant battery life of an apparatus, such as a mobile telephone, is to measure the battery voltage and then read an extant battery life value from a pre-programmed lookup table. This has the advantage of being relatively simple to implement but suffers from a lack of accuracy.
This problem is addressed in GB-A-2312517 which describes taking three voltage readings, fitting a discharge curve to the readings and then determining the extant battery life from the curve fitted to the readings. This approach is more accurate that the earlier lookup table technique. However, it is computationally intensive since the parameters of a formula for determining the battery discharge time to a specified voltage must be repeatedly calculated. It should be noted that these calculations are not trivial.
Some saving in computation can be made by storing pre-calculated values for the parameters of a battery discharge model formula. However, the calculation of these parameters requires lengthy discharge tests of many batteries having different chemistries and capacities for each of the characteristic operating currents of the device, e.g. idle and active modes of a mobile phone. The fact that it takes 18 days for a 900 mAh battery to discharge at a constant current of 2 mA gives some idea of the problem when one considers that the characteristic current may be constantly changing during the development of a product.
According to the present invention, there is provided a battery powered apparatus comprising a battery, a memory storing a set of parameter values appropriate for calculating a total life estimate of a reference battery according to an algorithm and processing means programmed to estimate the extant life of said battery of the apparatus by scaling at least one of said parameter values in dependence on the capacity of said battery of the apparatus and calculating a total life estimate for said battery of the apparatus using the or each scaled parameter value and said algorithm.
Thus, the apparatus does not need to be programmed with so many parameter values.
Preferably, said battery of the apparatus includes means identifying its capacity and the processing means comprises means for determining the capacity of said battery from said capacity identifying means. This means that a new battery can be introduced for the device after the end of its development.
Preferably, the processing means is programmed to implement said algorithm by calculating said total life estimate for the battery of the apparatus using the formula:       ln    ⁢          (                        ϕ          -                      V            low                          ζ            )            ln    ⁢          xe2x80x83        ⁢    α  
where xcfx86, xcex6 and xcex1 constitute parameters for which said default values are stored in the memory and Vlow is a battery voltage indicative of the battery of the apparatus approaching an empty state. More preferably, the processing means is programmed to scale the parameter xcex1 according the capacity of the battery by implementing the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              C            default                                C            new                              ]        +    1  
where Cdefault is the capacity of the reference battery and Cnew and the value of xcex1default being one of said default parameter values stored in the memory.
The reduction in the amount of battery testing that may be achieved is primarily a benefit for the manufacturing process.
According to the present invention, there is provided a method of manufacturing a battery powered apparatus having processing means, the method comprising:
discharging a battery at a constant current and recording the voltage across the battery as it discharges;
determining default parameter values for a battery discharge model for estimating total battery life from the recorded voltages; and
programming said processing means with a program implementing said model and the values of said parameter values,
wherein the programming means is programmed to scale the product of the application of said model in dependence on a current demand value dependent on said apparatus.
Preferably, a manufacturing method according to the present invention comprises:
discharging a battery, of the same type, at a further constant current and recording the voltage across the battery as it discharges;
determining further default parameter values for the battery discharge model for estimating total battery life from the recorded voltages for said further constant current discharge,
wherein the model parameter values programmed into the processing means are selected from said determined default parameter values in dependence on said apparatus dependant current value.
According to the present invention, there is provided a method of manufacturing a plurality of different battery powered apparatuses having respective processing means and different current demands, the method comprising:
discharging a battery or a plurality of batteries of the same type at a plurality of different constant currents and recording the voltage across the or each battery as it discharges;
for each discharge current, determining default parameter values for a battery discharge model for estimating total battery life from the recorded voltages; and
for each apparatus, programming its processing means with a program implementing said model and the default parameter values for the discharge current nearest to a respective apparatus dependent current demand value,
wherein each programming means is programmed to scale the product of the application of said model in dependence on the relevant current demand value.
Preferably, in a manufacturing method according to the present invention, the parameters are for a model of the form:       ln    ⁢          (                        ϕ          -                      V            low                          ζ            )            ln    ⁢          xe2x80x83        ⁢    α  
where xcfx86, xcex6 and xcex1 constitute parameters for which said default values are stored in the memory and Vlow is a battery voltage indicative of the battery of the apparatus approaching an empty state. More preferably, said scaling comprises scaling the default value of the parameter xcex1, stored in the memory.
If the or each battery is a Li-ion battery, the or each processing means is preferably programmed to scale the default value of xcex1 according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                I            default                              ]        +    1  
where Iexp is said apparatus dependent current value and Idefault is the respective discharge current for which the parameter values, programmed into the or each apparatus, were determined.
If the or each battery is a NiMH battery, the or each processing means is preferably programmed to scale the default value of xcex1 according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                              I              default                        ·                          (                              1                -                X                            )                                          ]        +    1  
if the apparatus dependent current is greater than that relating to the programmed parameter value and according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                              I              default                        ·                          (                              1                +                X                            )                                          ]        +    1  
if the apparatus dependent current is less than that relating to the programmed parameter value,
where Iexp is said apparatus dependent current value and Idefault is the respective discharge current for which the parameter values, programmed into the or each apparatus, were determined. Preferably, is about 0.05.
According to the present invention, there is also provided a battery powered apparatus comprising a battery and processing means configured for calculating an extant battery life estimate for the battery using a battery discharge model, wherein the product of the use of said model is scaled by the processing means in dependence on a current demand value for the apparatus.
Preferably, the model is of the form:       ln    ⁢          (                        ϕ          -                      V            low                          ζ            )            ln    ⁢          xe2x80x83        ⁢    α  
and the processing means is programmed with default values for xcfx86, xcex6, xcex1 and Vlow and the value for a used is derived from the programmed default value for xcex1 in dependence on said current demand value, and Vlow is a battery voltage indicative of the battery of the apparatus approaching an empty state.
If the battery is a Li-ion battery, the value of the parameter xcex1 used is preferably determined according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                I            default                              ]        +    1  
where Iexp is said apparatus dependent current value and Idefault is the respective discharge current for which the parameter values, programmed into the or each apparatus, were determined.
If the battery is a NiMH battery, the value of the parameter xcex1 used is preferably determined according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                              I              default                        ·                          (                              1                -                X                            )                                          ]        +    1  
where Iexp is said apparatus dependent current value and Idefault is the respective discharge current for which the parameter values, programmed into the or each apparatus, were determined and is less than Iexp and/or the value of the parameter xcex1 used is scaled according to the formula:   α  =            [                        (                                    α              default                        -            1                    )                ·                              I            exp                                              I              default                        ·                          (                              1                +                X                            )                                          ]        +    1  
where Iexp is said apparatus dependent current value and Idefault is the respective discharge current for which the parameter values, programmed into the or each apparatus, were determined and is greater than Iexp. Preferably, X is about 0.05.
According to the present invention, there is further provided a battery-powered apparatus including a battery voltage sensor for sensing the voltage of a battery powering the apparatus and processing means, wherein the processing means is configured to estimate the extant life of a battery powering the apparatus by:
using a battery voltage value, derived from the voltage measured by said sensor, and a battery discharge elapsed time value to determine whether the value of a dominating parameter of a function, derived from a model of a substantial part of the discharging of a battery, meets a fitness criterion; and
if the value of said dominating parameter fails to meet said fitness criterion, modifying said dominating parameter""s value in a predetermined manner and then calculating an estimate of extant battery life using said function. The modification of the dominating parameter has been found to be particularly useful for ensuring that the battery life estimates remain appropriate as a battery ages.
Preferably, the processing means is configured to modify the value of a further parameter of said function if said dominating parameter""s value fails to meet said fitness criterion.
Preferably, the processing means is configured to generate said elapsed time value is by scaling a measured time value using a function of battery load current.
Preferably, the processing means is configured to select an expected load current value from a collection of load current values indexed by operating modes of the apparatus. An alternative would be to use a measured value.
Advantageously, said function is of the form:       t    r    =      (                            ln          ⁢                      xe2x80x83                    ⁢                                    ϕ              -                              V                low                                      ζ                                    ln          ⁢                      xe2x80x83                    ⁢          α                    -              t        elap              )  
where tr is the extant battery life value, xcfx86 is said dominating parameter, xcex1 and xcex6 are further parameters, Vlow is a battery voltage indicative of the battery approaching an empty state, and elap is said elapsed time value, and said model relates battery voltage to discharge time at constant current thus:
Vb=xcfx86xe2x88x92xcex6xcex1telap.
and preferably, said fitness criterion is:
xcex94xcfx86acceptable greater than Vb+xcex6xcex1telapxe2x88x92xcfx86
where Vb is the current battery voltage value. Preferably, xcex94xcfx86acceptable is in the range 0.04V to 0.06V, preferably 0.05V.
Said battery is preferably connected to said apparatus and may be, for example, a Li-ion or NiMH battery.
According to the present invention, there is further provided a mobile phone including a battery, a voltage sensor for measuring the voltage of the battery and a processor configured to control the mobile phone for operation in a standby mode and in a non-standby mode, the processor being further configured to estimate the extant life of said battery in said standby mode by an extant battery life estimating process comprising:
using a battery voltage value, derived from the voltage measured by said sensor, and a battery discharge elapsed time value to determine whether the value of a dominating parameter of a function, derived from a model of a substantial part of the discharging of a battery, meets a fitness criterion; and
if the value of said dominating parameter fails to meet said fitness criterion, modifying said dominating parameter""s value in a predetermined manner and calculating an estimate of extant battery life using said function.
Preferably, said function is of the form:       t    r    =      (                            ln          ⁢                      xe2x80x83                    ⁢                                    ϕ              -                              V                low                                      ζ                                    ln          ⁢                      xe2x80x83                    ⁢          α                    -              t        elap              )  
where tr is the extant battery life value, xcfx86 is said dominating parameter, xcex1 and xcex6 are further parameters, Vlow is a battery voltage indicative of the battery approaching an empty state, telap is said elapsed time value, and said model relates battery voltage to discharge time at constant current thus:
Vb=xcfx86xe2x88x92xcex6xcex1telap.
The mobile phone may employ parameter scaling in dependence on battery capacity according to the present invention, in which case said process comprises initially determining whether it is being run for a first time since the mobile phone was powered up and, if so, setting the value of at least one of said parameters in dependence on the capacity of the battery.
The mobile phone may employ parameter scaling in dependence on current demand according to the present invention, in which case the processor is configured to control the mobile phone to operate according to a plurality of communication protocols and said process comprises initially determining whether it is being run for a first time since the mobile phone was powered up and, if so, setting the value of the parameter xcex1 by scaling a default value according to the expected standby current demand for the communication protocol currently being used.
Preferably, said process comprises determining whether the mobile phone is in standby mode and, if so, performing a first routine otherwise performing a second routine.
Preferably, the first routine comprises:
updating telap;
determining that the battery is neither low nor high;
calculating xcex94xcfx86 where xcex94xcfx86=Vb+xcex6xcex1telapxe2x88x92xcfx86;
determining whether this is the first time that standby mode has been entered and, if so,
updating said parameters according to             ϕ      new        =                  ϕ        old            +              0.1        ⁢        Δϕ                        α      new        =                  α        old            -                        Δϕ          ⁡                      [                                                            α                  0                                -                1                                            ϕ                0                                      ]                          ·        2                        ζ      new        =                  ζ        old            +                        Δϕ          ⁡                      [                                          ζ                0                                            ϕ                0                                      ]                          ·        2            
else
determining whether xcex94xcfx86 is greater then xcex94xcfx86acceptable and, if so
updating said parameters according to             ϕ      new        =                  ϕ        old            +                        [                      Δϕ            -                                                            "LeftBracketingBar"                  Δϕ                  "RightBracketingBar"                                Δϕ                            ·                              Δϕ                acceptable                                              ]                ·                  μ          ϕ                                α      new        =                  α        old            -              Δϕ        ·                  μ          α                                        ζ        new            =                        ζ          old                -                  Δϕ          ·                      μ            ζ                                ;  
and
calculating tr,
wherein xcex94xcfx86acceptable and xcexcxcfx86 are predetermined and xcexcxcex6 and xcexcxcex1 are set according to             μ      α        =                  (                                            α              0                        -            1                                ϕ            0                          )            ·      0.5                  μ      ζ        =                  (                              ζ            0                                ϕ            0                          )            ·              0.5        .            
Preferably, the second routine comprises:
determining whether the battery voltage indicated a full battery when last measured and, if so
estimating the prevailing load current on the basis of the current operational status, e.g. protocol, modulation method, PDA functions;
estimating the equivalent standby battery voltage for the present value of telap;
determining whether said equivalent standby battery voltage indicates a full battery and, if not:
updating updating xcfx86 according to xcfx86new=xcfx86old+0.5xcex94xcfx86 with xcex94xcfx86
being derived using the equivalent standby battery voltage;
else
estimating the load current according to       I    load    =                    [                  ϕ          +                      ζα                          t              elap                                      ]            -              V        b                    R      b      
xe2x80x83where Rb is an approximate value for the resistance of the battery and Vb is the measured battery voltage;
calculating a value for said elapsed time value by calculating an incremental elapsed time value according to       Δ    ⁢          xe2x80x83        ⁢          t      elap        =                    (                  1          +                                    I              load                                      I              min_stby                                      )            ·      Δ        ⁢          xe2x80x83        ⁢          t      elap_measured      
xe2x80x83where Iminxe2x80x94stby is the minimum expected standby current;
calculating tr.
In the present document, the term xe2x80x9cfullxe2x80x9d when applied to a battery means a battery sufficiently charged that its voltage is above a threshold in the region of the battery""s discharge characteristic where the transition from the initial rapidly dropping voltage to the more gently dropping voltage.